Extrusion resistant gasket face seal

ABSTRACT

A seal assembly for a fluid coupling includes: (a) a generally planar, substantially rigid seal retainer with opposed first and second faces, having an annular first groove formed in the first face; (b) a first resilient seal disposed in the first groove; and (c) an annular first backup ring positioned radially outboard of the first resilient seal and secured to the first resilient seal, wherein the first backup ring is substantially harder than the first resilient seal.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

The U.S. Government may have certain rights in this invention pursuantto contract number N00019-96-C-0176 awarded by the Department of theNavy.

BACKGROUND OF THE INVENTION

This invention relates generally to fluid couplings and moreparticularly to sealing arrangements for fluid couplings.

Certain aircraft gas turbine engines employ fluid systems operating athigher than average pressures, and are thus prone to leakage. Forexample, in some applications, fuel at 28 MPa (4000 psi) is used as aworking fluid to operate multiple engine actuators. Because of the highpressures and high fuel flows, a type of coupling known as a 4-boltflange face seal is used to make fluid connections between the variouscomponents. Based upon extrusion analysis, a standard type of seal wouldrequire a thicker flange than what is normally used in moderate-pressuresystems, in order to prevent the flange from lifting off the seal. Thisthicker flange adds weight to the overall design and the seal will stillbe susceptible to failure if the flange is not clamped properly duringassembly.

Historically, 4-bolt flange face seals would incorporate one of twotypes of seal designs: (1) a combination metal and elastomer flangegasket, such as those sold under the GASK-O-SEAL brand name by ParkerHannifin Company, Cleveland, Ohio 44124 USA; or (2) a loose L-shapedcross-section elastomer seal with a mating backup ring. The standardflange gasket consists of a metal retainer plate with an elastomer sealon each side. The seal is permanently attached to the retainer plate forsimplification in maintainability and assembly. One side of the seal iscompressed against the flange and the other seal is compressed againstthe mating component or flange. The negative aspect of the flange gaskettype design is that it is limited under high pressures and requires asmall clearance gap to be maintained to prevent seal extrusion. Thisrequires a thick, stiff flange connection to limit bending in theflange.

The loose L-shaped elastomer sits in a seal gland in the matingcomponent or flange. A flange is then clamped over the seal to provide acompression force on the seal. This design has maintainabilitylimitations, as there is no visual indicator that verifies that the sealis installed in the seal gland. The seal can also be installed in aninverted position that will cause the backup ring to be in the bottom ofthe gland, rendering it useless during operation. This type of seal alsorequires precision-machined glands in the flange for proper operation.

BRIEF SUMMARY OF THE INVENTION

These and other shortcomings of the prior art are addressed by thepresent invention, which provides a bolted flange gasket sealincorporating an integral anti-extrusion feature.

According to one aspect, a seal assembly for a fluid coupling includes:(a) a generally planar, substantially rigid seal retainer with opposedfirst and second faces, having an annular first groove formed in thefirst face; (b) a first resilient seal disposed in the first groove; and(c) an annular first backup ring positioned radially outboard of thefirst resilient seal and secured to the first resilient seal, whereinthe first backup ring is substantially harder than the first resilientseal.

According to another aspect of the invention a fluid coupling includes:(a) a first ferrule having a bore passing therethrough and a sealingface disposed at one end thereof; (b) a second ferrule having a borepassing therethrough and a sealing face disposed at one end thereof; (c)a generally planar, substantially rigid seal retainer clamped betweenthe sealing faces of the ferrules, the seal retainer having opposedfirst and second faces, each face having an annular groove formedtherein; and (d) a seal ring disposed in each of the grooves,comprising: (i) a resilient annular seal; and (ii) an annular backupring positioned radially outboard of the resilient seal and secured tothe resilient seal, wherein the backup ring is substantially harder thanthe resilient seal.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be best understood by reference to the followingdescription taken in conjunction with the accompanying drawing figuresin which:

FIG. 1 is a side view of a fluid coupling constructed according to anaspect of the present invention;

FIG. 2 is an exploded half-sectional view of the fluid coupling of FIG.1;

FIG. 3 is a perspective view of a seal assembly shown in FIG. 1;

FIG. 4 is a half-sectional view of the seal assembly of FIG. 3; and

FIG. 5 is an enlarged half-sectional view of the tubing joint in anassembled condition.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings wherein identical reference numerals denotethe same elements throughout the various views, FIG. 1 depicts a fluidcoupling assembly 10 comprising a first conduit 12 connected to a firstferrule 14 and a second conduit 16 connected to a second ferrule 18. Aseal assembly 20 is disposed between the ferrules 14 and 18. Theferrules 14 and 18 are clamped together between a pair of plate-likeflanges 22 and 24, which are secured with clamping means such as theillustrated bolts 26. In the illustrated example, the first and secondconduits 12 and 16 comprise metallic tubing carrying fluid used as ahigh pressure hydraulic working fluid in a gas turbine engine, forexample at about 28 MPa (4000 psi). The principles of the presentinvention are applicable anywhere a reliable fluid face seal isrequired.

FIG. 2 is a half-sectional, exploded view of the components of the fluidcoupling 10. The first ferrule 14 is substantially rigid and may beconstructed from a material such as a steel or aluminum alloy. It has agenerally cylindrical body 28 with first and second ends 30 and 32, anda central bore 34 passing therethrough. A sealing face 36 is disposed atthe first end 30. An annular rim 38 extends radially outward from thebody 28. The first conduit 12, which may be pipe or tubing of a knowntype, has an open end 40 which is joined to the second end 32 of thefirst ferrule 14 in a fluid-tight joint, for example using fasteners,adhesives, or thermal or sonic bonding. In the illustrated example thefirst conduit 12 and the first ferrule 14 are joined by a butt weld.

The second ferrule 18 and the second conduit 16 are identical inconstruction to the first ferrule 14 and the first conduit 12,respectively, and they are joined to each other in a similar manner.

FIGS. 3 and 4 illustrate the construction of the seal assembly 20. Itincludes a substantially rigid, generally planar seal retainer 42 withopposed first and second faces 44 and 46, and a central opening 48 forpassing fluid flow. Examples of suitable materials for the seal retainer42 include steel and aluminum alloys. Annular grooves 48 and 50 areformed in the first and second faces 44 and 46, respectively. Identicalseal rings 52 are disposed in the grooves 48 and 50.

The seal ring 52 comprises a resilient seal 56 and a backup ring 58. Theresilient seal 56 may be constructed from any resilient material whichis compatible with the expected physical and chemical conditions to beencountered in operation. In the illustrated application, which isintended for use with high-pressure liquid hydrocarbon fuel, afluorocarbon polymer such as polytetrafluoroethylene (PTFE) is oneexample of a suitable material. The hardness (Durometer) rating of theresilient seal 56 will vary depending upon the application, with softermaterials being used where low ambient temperatures are expected. In theillustrated example, the resilient seal 56 has a hardness of about 75 onthe Shore “A” scale. The resilient seal 56 is generally “L”-shaped incross-section, with a radial leg 60 and an axial leg 62. The axial leg62 has a convex, rounded distal end, and is sized to protrude from thefirst face 44 of the seal retainer 42 in the free state. The amount ofprotrusion is determined by the amount of compression that is desiredwhen the fluid coupling 10 is assembled.

The backup ring 58 is positioned in the “corner” formed by the radialand axial legs 60 and 62. The backup ring 58 is secured to the resilientseal 56. Examples of suitable methods of securing the two componentsinclude fasteners, adhesives, thermal or sonic bonding, and co-moldingof the resilient seal 56 and the backup ring 58. The backup ring 58 ismade harder than the resilient seal 56 in order to prevent the resilientseal 56 from extruding between the components of the fluid coupling 10under pressure. In the illustrated example, any material having ahardness of about 90 Shore A or greater would be sufficient for thispurpose. Many known plastics and metals can meet this hardnessrequirement.

Optionally, the seal rings 52 may be secured in the grooves 48 and 52,for example using fasteners or adhesives. This makes the seal assembly20 an integral unit.

FIG. 5 shows the fluid coupling 10 in an assembled condition, with theseal assembly 20 clamped between the first and second ferrules 14 and18, which are in turn clamped by the flanges 22 and 24. The seal rings52 are disposed in the grooves 48 and 50. The resilient seals 56 arecompressed and the backup rings 58 are positioned outboard of theresilient seals 56, so they can resist outwards extrusion of theresilient seals 56. It is impossible for the backup rings 58 to beinadvertently omitted from the seal assembly 20, because they aresecured to the resilient seals 56 as described above. Furthermore, thenature of the L-shaped cross-section of the resilient seals 56 makes itimmediately obvious if they have been installed in an inverted position.In the case where the seal rings 52 are secured to the seal retainer 42,it is impossible to omit the seal rings 52 from the assembly. The sealassembly 20 is symmetrical, so it is further impossible to incorrectlyassemble the fluid joint 10.

There are several advantages to the seal assembly described abovecompared to prior art flange seals, namely: (1) reduced fitting weight,(2) increased reliability of the seal, (3) easy visual verification of aproperly installed seal, (4) reduced maintenance induced failures fromincorrect seal installation, (5) improved maintainability from the useof minimal parts, and reduced cost from simplification of the 4 boltflange manufacturing process. These benefits will allow for a lighter,more maintainable, and an improved reliability seal configuration.

The foregoing has described a fluid coupling configuration and sealassembly. While specific embodiments of the present invention have beendescribed, it will be apparent to those skilled in the art that variousmodifications thereto can be made without departing from the spirit andscope of the invention. Accordingly, the foregoing description of thepreferred embodiment of the invention and the best mode for practicingthe invention are provided for the purpose of illustration only and notfor the purpose of limitation.

1. A seal assembly for a fluid coupling, comprising: (a) a generallyplanar, substantially rigid seal retainer with opposed first and secondfaces, having an annular first groove formed in the first face; (b) afirst resilient seal disposed in the first groove; and (c) an annularfirst backup ring positioned radially outboard of the first resilientseal and secured to the first resilient seal, wherein the first backupring is substantially harder than the first resilient seal.
 2. The sealassembly of claim 1 wherein the first resilient seal is secured in thefirst groove.
 3. The seal assembly of claim 1 wherein: (a) the firstresilient seal has a generally L-shaped cross-sectional shape withaxially and radially-extending legs; and (b) the first backup ring ispositioned in a corner defined by the radial and axial legs.
 4. The sealassembly of claim 3 wherein the axially-extending leg has a convex,curved distal end.
 5. The seal assembly of claim 1 wherein theaxially-extending leg extends past the first face of the seal retainerin a free state.
 6. The seal assembly of claim 1 wherein the firstresilient seal comprises a fluorocarbon elastomer.
 7. The seal assemblyof claim 1 wherein the first resilient seal has a hardness of about 75Shore A or less.
 8. The seal assembly of claim 1 wherein the firstbackup ring has a hardness of about 90 shore A or greater.
 9. The sealassembly of claim 1 wherein the seal retainer includes an annular secondgroove formed in the second face, the seal assembly further comprising:(a) a second resilient seal disposed in the second groove; and (b) anannular second backup ring positioned radially outboard of the secondresilient seal and secured to the second resilient seal, wherein thesecond backup ring is substantially harder than the second resilientseal.
 10. The seal assembly of claim 9 wherein the second resilient sealis secured in the second groove.
 11. A fluid coupling, comprising: (a) afirst ferrule having a bore passing therethrough and a sealing facedisposed at one end thereof; (b) a second ferrule having a bore passingtherethrough and a sealing face disposed at one end thereof; (c) agenerally planar, substantially rigid seal retainer clamped between thesealing faces of the ferrules, the seal retainer having opposed firstand second faces, each face having an annular groove formed therein; and(d) a seal ring disposed in each of the grooves, comprising: (i) aresilient annular seal; and (ii) an annular backup ring positionedradially outboard of the resilient seal and secured to the resilientseal, wherein the backup ring is substantially harder than the resilientseal.
 12. The fluid coupling of claim 11 wherein the seal rings aresecured in the grooves.
 13. The fluid coupling of claim 11 furthercomprising: (a) A first flange which bears against the first ferrule;(b) A second flange which bears against the second ferrule; and (c)clamping means securing the flanges together.
 14. The fluid coupling ofclaim 13 wherein the clamping means comprise mechanical fastenersinterconnecting the first and second flanges.
 15. The fluid coupling ofclaim 11 further comprising: (a) a first conduit secured in fluidcommunication with the first ferrule; and (b) a second conduit securedin fluid communication with the second ferrule.
 16. The fluid couplingof claim 11 wherein: (a) each of the resilient seals has a generallyL-shaped cross-sectional shape with axially and radially-extending legs;and (b) the corresponding backup ring of each seal is positioned in acorner defined by the radial and axial legs.
 17. The fluid coupling ofclaim 16 wherein the axially-extending leg of each resilient seal has aconvex, curved distal end.
 18. The fluid coupling of claim 16 whereinthe axially-extending leg extends past the face of the seal retainer ina free state.
 19. The fluid coupling of claim 11 wherein each of theresilient seals comprises a fluorocarbon elastomer.
 20. The fluidcoupling of claim 11 wherein each of the resilient seals has a hardnessof about 75 Shore A or less.
 21. The fluid coupling of claim 11 whereineach of the backup rings has a hardness of about 90 shore A or greater.